The major lethal proteins from two rattlesnakes venoms (Crotalus scutulatus scutulatus and Crotalus viridis concolor) will be purified to homogeneity. The physical and chemical properties of the purified toxins will be examined in detail. The studies will include determinations of molecular weights of the native toxins and of the subunits derived from the native toxins as well as composition, peptide mapping and sequence studies. Preparation of antibodies to the pure toxins will be attempted and immune sera will be examined for cross reactivity with venoms from other rattlesnake species. The arginine ester hydrolases from the venom of Crotalus scutulatus scutulatus will be purified. The specificities for substrates will be examined for each pure arginine esterase. An attempt will be made to identify some of the substances in host tissues that are subject to hydrolysis by the arginine esterases present in the venom from Crotalus scutulatus scutulatus.